A bearing (backing bearing) for use in back-up roll of rolling mill is in contact with a roll at its outer ring as a rotational ring and hence, the outer ring suffers fast deformation of its outside diameter surface or slip scars thereon, thus adversely affecting the thickness of a sheet material being rolled. Accordingly, the bearing requires frequent re-polishing of the outside diameter surface of its outer ring.
As a polishing jig for the outside diameter surface of the outer ring of the bearing for use in back-up roll of rolling mill, there has conventionally been known one disclosed in Japanese Examined Patent Publication No. 63-41704 (hereinafter, referred to as a prior art).
The polishing jig (re-polishing machine) of the prior art performs high accuracy polishing of the outside diameter surface of the outer ring by rotating only the outer ring via an engagement hole formed in the outer ring in a state where fit clearance/internal radial clearance of the bearing is eliminated by hydraulically protruding the polishing jig radially outwardly, the polishing jig on which an inner ring of the bearing is fitted.
However, a single conventional polishing jig can polish only one backing bearing, thus requiring much time to polish a large number of backing bearings. As a consequence, the conventional polishing jig suffers low efficiency.
According to the conventional polishing jig, the engagement hole (carrier hole) is previously formed at an axial end face of the outer ring of the bearing so as to be used to rotate the outer ring. During the polishing process, a carrier tip projected from a work head of a polishing machine is engageably inserted in the engagement hole for rotating the outer ring in unison with the work head. That is, the conventional polishing jig requires the engagement hole to be formed at the end face of the outer ring in order to rotate the outer ring. In a case where a bearing with no engagement hole formed at the end face is to be re-polished, there occurs a need to form the engagement hole, which results in low efficiency.
The present invention is directed to solution to the foregoing problem and has an object to provide a novel technical measure for achieving higher efficiency by improving the conventional polishing jig of a hydraulic integral system as the prior art.